Many vehicles such as boats and other marine crafts have fuel systems that require venting. For example, venting a fuel tank equalizes the pressure in the tank by releasing fuel vapors and allowing atmospheric air to flow into the fuel tank so that the liquid fuel can be drawn from the tank via suction. Some venting systems employ a separate venting tube or line to vent the fuel tank, while other venting systems employ a venting tube in combination with a filling device. Although a separate vent tube prevents the buildup of fuel pressure within the tank, it does not prevent contamination of the environment as a result of unintentional overboard venting of liquid fuel, which frequently occurs when a marine fuel tank is being refueled due to fuel tank overfilling and/or due to splashing, sloshing or other fuel surges during boat movement. Additionally, separate vent tubes are prone to allow the ingress of water and other contaminates into the fuel stored in the tank, which can lead to engine damage.
To prevent liquid fuel from escaping or passing through the venting tube due to tank overfilling and/or due to splashing, sloshing or other fuel surges, the vent tube and filling device are often combined and in fluid communication. Typically, boats are provided with a filling device integrally formed with a vent tube that can mount to a deck of the boat and connect to the fuel tank via fluid hoses and/or other conduits. In this manner, the combined filling device and vent tube prevents the unintentional overboard venting of liquid fuel during boat movements and returns fuel overflow to the tank in case of tank overfill. A combined vent tube and filling device typically requires a fuel cap that has a vent formed therein. Also, a vented fuel cap must typically allow adequate airflow through the fuel cap and prevent water and other contaminates from passing through the vent of the fuel cap and into the fuel tank.
Preventing the ingress of water through the fuel cap is important to prevent engine damage. However, allowing the venting of fuel vapors is also important to release the fuel vapors from the fuel tank and allow sufficient atmospheric airflow so that the liquid fuel in the tank can flow to the engine. Thus, a vented fuel cap typically requires a passageway in which the venting area is large enough to allow vapors and atmospheric air to pass therethrough, but small enough to prevent the ingress of water and other contaminates. However, a passageway that is small enough to prevent the ingress of water and other contaminates often provides an insufficient and ineffective venting area for venting atmospheric air and fuel vapors.